3-13 Up to three types of precipitation may be coded in a single present weather group. They are coded in order of decreasing dominance based on intensity.
3.1.5.8.5 Obscuration.
Obscurations are any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility in the atmosphere. The obscuration types are: mist (BR), fog (FG), smoke (FU), volcanic ash (VC), widespread dust (DU), sand (SA), haze (HZ), and spray (PY). Spray (PY) is coded only as BLPY.
With the exception of volcanic ash, low drifting dust, low drifting sand, low drifting snow, shallow fog, partial fog, and patches (of) fog, an obscuration is coded in the body of the report if the surface visibility is less than 7 miles (mi), or considered operationally significant. Volcanic ash is always reported when observed.
3.1.5.8.6 Other Weather Phenomena.
Other weather phenomena types include: well-developed dust/sand whirls (PO), sandstorms (SS), duststorms (DS), squalls (SQ), funnel clouds (FC), and tornados and waterspouts (+FC).
Examples:
-DZ Light drizzle -RASN Light rain and (light) snow SN BR (Moderate) snow, mist -FZRA FG Light freezing rain, fog SHRA (Moderate) rain shower VCBLSA Blowing sand in the vicinity -RASN FG HZ Light rain and (light) snow, fog, haze TS Thunderstorm (without precipitation) +TSRA Thunderstorm, heavy rain +FC TSRAGR BR Tornado, thunderstorm, (moderate) rain, hail, mist
3.1.5.9 Sky Condition Group.
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Sky condition is a description of the appearance of the sky. It includes either cloud cover, vertical visibility, or clear skies.
3-14 The sky condition group is based on the amount of cloud cover (the first three letters) followed by the height of the base of the cloud cover (final three digits). No space is between the amount of cloud cover and the height of the layer. The height of the layer is recorded in feet above ground level (AGL).
Sky condition is coded in ascending order and ends at the first overcast layer.
At mountain stations, if the layer is below station level, the height of the layer will be coded as ///.
Vertical visibility is coded as VV, followed by the vertical visibility into the indefinite ceiling. An indefinite ceiling is a ceiling classification applied when the reported ceiling value represents the vertical visibility upward into surface-based obscuration. No space is between the group identifier and the vertical visibility. Figure 3-3, Obscuration Effects on Slant Range Visibility, illustrates the effect of an obscuration on the vision from a descending aircraft.
Figure 3-3. Obscuration Effects on Slant Range Visibility
The ceiling is 500 ft in both examples, but the indefinite ceiling example (bottom) produces a more adverse impact to landing aircraft. This is because an obscuration (e.g., fog, blowing dust, snow) limits runway acquisition due to reduced slant range visibility. This pilot would be able to see the ground, but not the runway. If the pilot was at approach minimums, the approach could not be continued and a missed approach must be executed.
3-15 Clear skies are coded in the format SKC or CLR. When SKC is used, an observer indicates no layers are present; CLR is used by automated stations to indicate no layers are detected at or below 12,000 ft.
Each coded layer is separated from the others by a space. Each layer reported is coded by using the appropriate reportable contraction seen in Table 3-3, METAR/SPECI Contractions for Sky Cover. A report of clear skies (SKC or CLR) is a complete layer report within itself. The abbreviations FEW, SCT, BKN, and OVC will be followed (without a space) by the height of the layer.
Table 3-3. METAR/SPECI Contractions for Sky Cover Reportable Contraction Meaning Summation Amount of Layer VV Vertical Visibility 8/8 SKC or CLR1 Clear 0 FEW2 Few 1/8 – 2/8 SCT Scattered 3/8 – 4/8 BKN Broken 5/8 – 7/8 OVC Overcast 8/8
1. The abbreviation CLR will be used at automated stations when no layers at or below 12,000 ft are reported; the abbreviation SKC will be used at manual stations when no layers are reported.
2. Any layer amount less than 1/8 is reported as FEW.
The height is coded in hundreds of feet above the surface using three digits in accordance with Table 3-4, METAR/SPECI Increments of Reportable Values of Sky Cover Height.
Table 3-4. METAR/SPECI Increments of Reportable Values of Sky Cover Height Range of Height Values (feet) Reportable Increment (feet) Less than or equal to 5,000 To nearest 100 5,001 to 10,000 To nearest 500 Greater than 10,000 To nearest 1,000 The ceiling is the lowest layer aloft reported as broken or overcast. If the sky is totally obscured with ground-based clouds, the vertical visibility is the ceiling.
3-16 Figure 3-4. METAR/SPECI Sky Condition Coding
Clouds at 1,200 ft obscure 2/8ths of the sky (FEW). Higher clouds at 3,000 ft obscure an additional 1/8th of the sky, and because the observer cannot see above the 1,200-ft layer, he is to assume that the higher 3,000-ft layer also exists above the lower layer (SCT). The highest clouds at 5,000 ft obscure 2/8ths of the sky, and again since the observer cannot see past the 1,200 and 3,000-ft layers, he is to assume the higher 5,000-ft layer also exists above the lower layers (BKN).
The sky condition group would be coded as: FEW012 SCT030 BKN050.
At manual stations, cumulonimbus (CB) or towering cumulus (TCU) is appended to the associated layer. For example, a scattered layer of towering cumulus at 1,500 ft would be coded SCT015TCU, and would be followed by a space if there were additional higher layers to code.
Examples:
SKC No layers are present CLR No layers are detected at or below 12,000 ft AGL FEW004 Few at 400 ft AGL SCT023TCU Scattered layer of towering cumulus at 2,300 ft BKN100 Broken layer (ceiling) at 10,000 ft OVC250 Overcast layer (ceiling) at 25,000 ft VV001 Indefinite ceiling with a vertical visibility of 100 ft FEW012 SCT046 Few clouds at 1,200 ft, scattered layer at 4,600 ft
3-17 SCT033 BKN085 Scattered layer at 3,300 ft, broken layer (ceiling) at 8,500 ft SCT018 OVC032CB Scattered layer at 1,800 ft, overcast layer (ceiling) of cumulonimbus at 3,200 ft SCT009 SCT024 BKN048 Scattered layer at 900 ft, scattered layer at 2,400 ft, broken layer (ceiling) at 4,800 ft
3.1.5.10 Temperature/Dewpoint Group.
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Temperature is the degree of hotness or coldness of the ambient air, as measured by a suitable instrument. Dewpoint is the temperature to which a given parcel of air must be cooled at constant pressure and constant water vapor content for the air to become fully saturated.
Temperature and dewpoint are coded as two digits rounded to the nearest whole degree Celsius. For example, a temperature of 0.3 ºC would be coded at
00. Sub-zero temperatures and dewpoints are prefixed with an M. For example, a temperature of 4 ºC with a dewpoint of -2 ºC would be coded as 04/M02; a temperature of -2 ºC would be coded as M02.
If temperature is not available, the entire temperature/dewpoint group is not coded. If dewpoint is not available, temperature is coded followed by a solidus (/) and no entry is made for dewpoint. For example, a temperature of 1.5 ºC and a missing dewpoint would be coded as 02/.
3.1.5.11 Altimeter.
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The altimeter setting group codes the current pressure at elevation. This setting is then used by aircraft altimeters to determine the true altitude above a fixed plane of mean sea level (MSL).
The altimeter group always starts with an A and is followed by the four-digit group representing the pressure in tens, units, tenths, and hundredths of inches (in) of mercury. The decimal point is not coded. For example, an altimeter setting of 29.92 in of Mercury would be coded as A2992.
3.1.5.12 Remarks (RMK).
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
3-18 Remarks are included in METAR and SPECI, when appropriate.
Remarks are separated from the body of the report by the contraction RMK.
When no remarks are necessary, the contraction RMK is not required.
METAR/SPECI remarks fall into two categories: (1) Automated, Manual, and Plain Language, and (2) Additive and Automated Maintenance Data.
Table 3-5. METAR/SPECI Order of Remarks Automated, Manual, and Plain Language
1. Volcanic Eruptions
2. Funnel Cloud
3. Type of Automated Station
4. Peak Wind
5. Wind Shift
6. Tower or Surface Visibility
7. Variable Prevailing Visibility
8. Sector Visibility
9. Visibility at Second Location
10. Lightning
11. Beginning and Ending of Precipitation
12. Beginning and Ending of Thunderstorms
13. Thunderstorm Location
14. Hails tone Size
15. Virga
16. Variable Ceiling Height
17. Obscurations
18. Variable Sky Condition
19. Significant Cloud Types
20. Ceiling Height at Second Location
21. Pressure Rising or Falling Rapidly
22. Sea-Level Pressure
23. Aircraft Mishap
24. No SPECI Reports Taken
25. Snow Increasing Rapidly
26. Other Significant Information Additive and Automated Maintenance Data
27. Precipitation amount within a specified time period*
28. Cloud Types*
29. Duration of Sunshine*
30. Hourly Temperature and Dewpoint
31. 6-Hourly Maximum Temperature*
32. 6-Hourly Minimum Temperature*
33. 24-Hour Maximum and Minimum Temperature*
34. 3-Hourly Pressure Tendency*
35. Sens or Status Indicators
36. Maintenance Indicator Note: Additive data is primarily used by the National Weather Service for climatological purposes.
*These groups should have no direct impact on the aviation community and will not be discussed in this document.
Remarks are made in accordance with the following:
• Time entries are made in minutes past the hour if the time reported occurs during the same hour the observation is taken. Hours and minutes are used if the hour is different.
• Present weather coded in the body of the report as VC may be further described (e.g., direction from the station, if known). Weather phenomena beyond 10 sm of the point(s) of observation are coded as distant (DSNT) followed by the direction from the station. For example, precipitation of unknown intensity within 10 sm east of the station would be coded as VCSH E; lightning 25 sm west of the station would be coded as LTG DSNT W.
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• Distance remarks are in statute miles except for automated lightning remarks, which are in nautical miles (NM).
• Movement of clouds or weather, when known, is coded with respect to the direction toward which the phenomena are moving. For example, a thunderstorm moving toward the northeast would be coded as TS MOV NE.
• Directions use the eight points of the compass coded in a clockwise order.
• Inso far as possible, remarks are entered in the order they are presented in the following paragraphs (and Table 3-5, METAR/SPECI Order of Remarks).
3.1.5.13 Automated, Manual, and Plain Language Remarks.
These remarks generally elaborate on parameters reported in the body of the report. An automated station or observer may generate automated and manual remarks. Only an observer can provide plain language remarks.
3.1.5.13.1 Volcanic Eruptions (Plain Language).
Volcanic eruptions are coded in plain language and contain the following, when known:
• Name of volcano;
• Latitude and longitude or the direction and approximate distance from the station;
• Date/Time (UTC) of the eruption;
• Size description, approximate height, and direction of movement of the ash cloud; and
• Any other pertinent data about the eruption.
For example, a remark on a volcanic eruption would look like the following:
RMK MT. AUGUSTINE VOLCANO 70 MILES SW ERUPTED AT 231505 LARGE ASH CLOUD EXTENDING TO APRX 30000 FEET MOVING NE.
Pre-eruption volcanic activity is not coded. Pre-eruption refers to unusual and/or increasing volcanic activity which could presage a volcanic eruption.
3.1.5.13.2 Funnel Cloud.
At manual stations, tornadoes, funnel clouds, and waterspouts are coded in the following format: tornadic activity, TORNADO, FUNNEL CLOUD, or WATERSPOUT, followed by the beginning and/or ending time, followed by the location and/or direction of the phenomena from the station, and/or movement, when known. For example, TORNADO B13 6 NE would indicate
3-20 that a tornado began at 13 minutes past the hour and was 6 sm northeast of the station.
3.1.5.13.3 Type of Automated Station.
AO1 or AO2 is coded in all METAR/SPECI from automated stations.
Automated stations without a precipitation discriminator are identified as AO1; automated stations with a precipitation discriminator are identified as AO2.
3.1.5.13.4 Peak Wind.
Peak wind is coded in the following format: the remark identifier PK WND, followed by the direction of the wind (first three digits), peak wind speed (next two or three digits) since the last METAR, and the time of occurrence. A space is between the two elements of the remark identifier and the wind direction/speed group; a solidus (/), without spaces, separates the wind direction/speed group and the time. For example, a peak wind of 45 kts from 280 degrees that occurred at 15 minutes past the hour is coded PK WND 28045/15.
3.1.5.13.5 Wind Shift.
Wind shift is coded in the following format: the remark identifier WSHFT, followed by the time the wind shift began. The contraction FROPA is entered following the time if there is reasonable data to consider the wind shift was the result of a frontal passage. A space is between the remark identifier and the time and, if applicable, between the time and the frontal passage contraction. For example, a remark reporting a wind shift accompanied by a frontal passage that began at 30 minutes after the hour would be coded WSHFT 30 FROPA.
3.1.5.13.6 Tower or Surface Visibility.
Tower or surface visibility is coded in the following format: tower (TWR VIS) or surface (SFC), followed by the observed tower/surface visibility value. A space is coded between each of the remark elements. For example, the control tower visibility of 1½ sm would be coded TWR VIS 1 1/2.
3.1.5.13.7 Variable Prevailing Visibility.
Variable prevailing visibility is coded in the following format: the remark identifier VIS, followed by the lowest and highest visibilities evaluated, separated by the letter V. A space follows the remark identifier and no spaces are between the letter V and the lowest/highest values. For example, a visibility that was varying between ½ and 2 sm would be coded VIS 1/2V2.
3.1.5.13.8 Sector Visibility (Plain Language).
Sector visibility is coded at manual stations in the following format: the remark identifier VIS, followed by the sector referenced to eight points of the
3-21 compass, and the sector visibility in statute miles. For example, a visibility of 2½ sm in the northeastern octant is coded VIS NE 2 1/2.
3.1.5.13.9 Visibility at Second Location.
At designated automated stations, the visibility at a second location is coded in the following format: the remark identifier VIS, followed by the measured visibility value and the specific location of the visibility sensor(s) at the station. This remark will only be generated when the condition is lower than that contained in the body of the report. For example, a visibility of 2½ sm measured by a second sensor located at Runway 11 is coded VIS 2 1/2 RWY11.
3.1.5.13.10 Lightning.
When lightning is observed at a manual station, the frequency, type of lightning, and location are reported. The contractions for the type and frequency of lightning are based on Table 3-6, METAR/SPECI Type and Frequency of Lightning, for example, OCNL LTGICCG NW, FRQ LTG VC, or LTG DSNT W.
When lightning is detected by an automated system:
• Within 5 NM of the Airport Location Point (ALP), it is reported as TS in the body of the report with no remark.
• Between 5 and 10 NM of the ALP, it is reported as VCTS in the body of the report with no remark.
• Beyond 10 but less than 30 NM of the ALP, it is reported in remarks only as LTG DSNT followed by the direction from the ALP.
Table 3-6. METAR/SPECI Type and Frequency of Lightning Type of Lightning Type Contraction Definition Cloud-ground CG Lightning occurring between cloud and ground In-cloud IC Lightning which takes place within the cloud Cloud-cloud CC Streaks of lightning reaching from one cloud to another Cloud-air CA Streaks of lightning which pass from a cloud to the air, but do not strike the ground Frequency of Lightning Frequency Contraction Definition Occasional OCNL Less than 1 flash/minute Frequent FRQ About 1 to 6 flashes/minute Continuous CONS More than 6 flashes/minute
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3.1.5.13.11 Beginning and Ending of Precipitation.
At designated stations, the beginning and ending times of precipitation are coded in the following format: the type of precipitation, followed by either a B for beginning or an E for ending, and the time of occurrence. No spaces are coded between the elements. The coded times of the precipitation start and stop times are found in the remarks section of the next METAR. The times are not required to be in the SPECI. The intensity qualifiers are coded. For example, if rain began at 0005 and ended at 0030, and then snow began at 0020 and ended at 0055, the remarks would be coded RAB05E30SNB20E55. If the precipitation was showery, the remark is coded SHRAB05E30SHSNB20E55. If rain ended and snow began at 0042, the remark would be coded as RAESNB42.
3.1.5.13.12 Beginning and Ending of Thunderstorms.
The beginning and ending times of thunderstorms are coded in the following format: The thunderstorm identifier TS, followed by either a B for beginning or an E for ending, and the time of occurrence. No spaces are between the elements. For example, if a thunderstorm began at 0159 and ended at 0230, the remark is coded TSB0159E30.
3.1.5.13.13 Thunderstorm Location.
Thunderstorm locations are coded in the following format: the thunderstorm identifier TS, followed by the location of the thunderstorm(s) from the station, and the direction of movement, when known. For example, a thunderstorm southeast of the station and moving toward the northeast is coded TS SE MOV NE.
3.1.5.13.14 Hailstone Size.
At designated stations, the hailstone size is coded in the following format: the hail identifier GR, followed by the size of the largest hailstone. The hailstone size is coded in ¼ in increments. For example, GR 1 3/4 would indicate that the largest hailstones were 1¾ in. in diameter. If small hail or snow pellets, GS, are coded in the body of the report, no hailstone size remark is required.
3.1.5.13.15 Virga.
At designated stations, Virga is coded in the following format: the identifier VIRGA, followed by the direction from the station. The direction of the phenomena from the station is optional, e.g., VIRGA or VIRGA SW.
3.1.5.13.16 Variable Ceiling Height.
The variable ceiling height is coded in the following format: the identifier CIG, followed by the lowest ceiling height recorded, V denoting variability between two values, and ending with the highest ceiling height. A single space follows the identifier with no other spaces between the letter V and the lowest/highest ceiling values. For example, CIG 005V010 would indicate a ceiling is variable between 500 ft and 1,000 ft.
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3.1.5.13.17 Obscurations.
Obscurations, surface-based or aloft, are coded in the following format: the weather identifier causing the obscuration at the surface or aloft, followed by the sky cover of the obscuration aloft (FEW, SCT, BKN, OVC) or at the surface (FEW, SCT, BKN), and the height. Surface-based obscurations have a height of 000. A space separates the weather causing the obscuration and the sky cover; no space is between the sky cover and the height. For example, fog hiding 3/8 to 4/8 of the sky is coded FG SCT000; a broken layer at 2,000 ft composed of smoke is coded FU BKN020.
3.1.5.13.18 Variable Sky Condition.
Variable sky condition remarks are coded in the following format: the two operationally significant sky conditions (FEW, SCT, BKN, and OVC), separated by spaces, and V denoting the variability between the two ranges.
If several layers have the same condition amount, the layer height of the variable layer is coded. For example, a cloud layer at 1,400 ft varying between broken and overcast is coded BKN014 V OVC.
3.1.5.13.19 Significant Cloud Types.
At manual stations, significant cloud type remarks are coded in all reports.
3.1.5.13.20 Cumulonimbus.
Cumulonimbus not associated with thunderstorms is coded as CB, followed by the direction from the station, and the direction of movement, when known. The location, direction, and direction of movement entries are separated from each other by a space. For example, a CB up to 10 sm west of the station moving toward the east would be coded CB W MOV E. If the CB was more than 10 sm to the west, the remark is coded CB DSNT W.
Cumulonimbus (CB) always evolves from the further development of towering cumulus (TCU). The unusual occurrence of lightning and thunder within or from a CB leads to its popular title, thunderstorm. A thunderstorm usually contains severe or greater turbulence, severe icing, and Low-Level Wind Shear (LLWS).
3.1.5.13.21 Towering Cumulus.
Towering cumulus clouds are coded in the following format: the identifier TCU, followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, a towering cumulus cloud up to 10 sm west of the station is coded TCU W.
3.1.5.13.22 Standing Lenticular or Rotor Clouds.
Stratocumulus (SCSL), altocumulus (ACSL), cirrocumulus (CCSL), or rotor clouds are coded in the following format: the cloud type followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, altocumulus standing lenticular clouds observed southwest through west of the station are coded ACSL SW-W; an apparent
3-24 rotor cloud 5 to 10 sm northeast of the station is coded APRNT ROTOR CLD NE; and cirrocumulus clouds south of the station are coded CCSL S.
3.1.5.13.23 Ceiling Height at Second Location.
At designated stations, the ceiling height at a second location is coded in the following format: the identifier CIG, followed by the measured height of the ceiling and the specific location of the ceilometer(s) at the station. This remark is only generated when the ceiling is lower than that contained in the body of the report. For example, if the ceiling measured by a second sensor located at Runway 11 is broken at 200 ft, the remark would be coded CIG 002 RWY11.
3.1.5.13.24 Pressure Rising or Falling Rapidly.
At designated stations, the reported pressure is evaluated to determine if a pressure change is occurring. If the pressure is rising or falling at a rate of at least 0.06 in per hour and the pressure change totals 0.02 in or more at the time of the observation, a pressure change remark is reported. When the pressure is rising or falling rapidly at the time of observation, the remark pressure rising rapidly (PRESRR) or pressure falling rapidly (PRESFR) is included in the remarks.
3.1.5.13.25 Sea-Level Pressure.
At designated stations, the sea-level pressure is coded in the following format: the identifier SLP, immediately followed by the sea-level pressure in millibars (mb)1. The hundreds and thousands units are not coded and must be inferred. For example, a sea-level pressure of 998.2 mb is coded SLP982. A sea-level pressure of 1,013.2 mb would be coded SLP132. For a METAR, if sea-level pressure is not available, it is coded SLPNO.
3.1.5.13.26 Aircraft Mishap.
If a SPECI report is taken to document weather conditions when notified of an aircraft mishap, the remark ACFT MSHP is coded in the report, but the SPECI is not transmitted.
3.1.5.13.27 No SPECI Reports Taken (Plain Language).
At manual stations where SPECIs are not taken, the remark NOSPECI is coded to indicate no changes in weather conditions will be reported until the next METAR.
3.1.5.13.28 Snow Increasing Rapidly.
At designated stations, the snow increasing rapidly remark is reported in the next METAR whenever the snow depth increases by 1 in or more in the past hour. The remark is coded in the following format: the remark indicator
1 Although the international unit of pressure measurement is now the Pascal, we will use the term millibar in this document version because, at this time, it is felt the reader is probably more familiar with millibars. Increasingly in meteorology literature, however, the term hectopascal (hPa) has replaced the term millibar to conform to international standards and because 1 hPa = 1 mb.